deserts and arid regions

Deserts and Arid Regions

Desert• Region with low precipitation

– Usually less than 25 cm of rain per year• Distribution

– Most related to descending air masses– Belts at 30o North & South latitude– Rain shadow of mountains– Great distance from oceans– Tropical coasts next to cold ocean currents– Polar desserts

Some characteristics of deserts

• Lack of through-flowing streams• Internal drainage• Desert thunderstorms

– Flash floods• Mudflows

Some characteristics of deserts

• Stream channels normally dry– Covered with sand & gravel– Narrow canyons with vertical walls

• Resistance of rocks to weathering– Desert topography typically steep and angular

Desert Features in S.W. United States

• Mojave Desert, CA• Basin and Range, NV• Colorado Plateau

Numbers indicate rainfall

Alluvial Fans

Desert Features in S.W. United States

– Colorado Plateau• Mostly flat-lying sedimentary beds• Plateaus, mesas, buttes

Wind Action• Strong in desert because:

– Low humidity– Great temperature ranges– More effective because of lack of vegetation

• Effective erosion in deserts because sediment is dry

Wind Erosion and Transportation

• Dust storms• Sand

– Moves along ground- saltation– Sandstorms– Sandblasting up to 1 meter

• Ventifact

• Deflation Pavement– Blowout

Wind Deposition

• Loess• Sand Dunes

– Well-sorted, well-rounded sand grains– Slip face

• Angle of repose– Wind ripples